As storage containers for various medicaments such as drugs, so-called vials have been widely used over years. As these vials, two types are employed, one being glass-made vials and the other plastic-made vials. Of these, the glass-made vials are equipped with very high gas barrier properties compared with the plastic-made vials, and therefore, are used as medicament containers for which high gas barrier properties are required.
After a medicament is stored in such a vial, its mouth is sealed with a plug such as a rubber plug. When the vial is subjected to treatment such as heat sterilization, the plug may slip out of the vial mouth due to a rise in the internal pressure of the vial. It is, therefore, a common practice to fit a cap, which is made of aluminum or a plastic, on the mouth of the vial such that the cap encloses the plug therein and extends onto an underside of a lip of the mouth to keep the plug in close contact with the mouth, to prevent the separation of the plug and to assure the sealing of an interior of the vial (JP-A-2007-282891).
An aluminum-made cap is crimped at a lower part thereof below the lip of the mouth of the vial by making use of its superb deformability, and therefore, is equipped with excellent separation-preventing properties. An aluminum-made cap is, however, accompanied by a problem that fine aluminum particles occur and scatter through its contact with other aluminum-made caps and also by a problem that segregated disposal of aluminum is difficult after its use. There is, accordingly, a tendency to avoid the use of aluminum-made caps in recent years.
A plastic-made cap, on the other hand, is free of such problems of the aluminum-made cap, but due to the lower deformability of a plastic than aluminum, is accompanied by a problem that its engagement with a vial cannot be as tight as that available from an aluminum-made cap. Described specifically, when an aluminum-made cap is crimped at a lower part thereof on a lip of a vial mouth, the lower part is caused to deform along the lip and is readily crimped by making use of its excellent deformability. In the case of a plastic-made cap, on the other hand, the cap is provided with engagement claws, and upon capping, these claws are brought into engagement with a lip of a vial mouth. The above-described problem of the plastic-made cap can be attributed to the above-mentioned difference in structure.
The plastic-made cap easily separates from the vial because the engagement between the vial and the plastic-made cap is not tight as described above. This problem can be solved if the engagement between the vial and the cap is made tight. However, the capping itself becomes harder as an attempt is made to establish tighter engagement. As appreciated from the foregoing, the cap and the vial are both required to have high dimensional accuracy. If a cap and a vial are both made of plastics, their dimensional accuracy can be improved to certain extent because they can be molded into predetermined shapes while taking into consideration even shrinkage deformations which take place upon cooling.
On the other hand, a glass-made vial has a dimensional error greater by one digit than a plastic-made vial because it is produced while adjusting its shape. No matter how much the dimensional accuracy of a plastic-made cap is improved, its application to a glass-made vial still involves a problem that the separation of the cap can be hardly prevented to sufficient extent. Under these circumstances, extremely high dimensional accuracy is required for both of a glass-made vial and a plastic-made vial to bring the plastic-made cap into tight engagement with the glass-made vial compared with the engagement of an aluminum-made cap. There is, however, a limitation to how much the dimensional accuracy of the glass-made vial can be improved. Even if plastic-made caps are provided with high dimensional accuracy, they are hence accompanied by a problem that, when they are applied to glass-made vials, the percentage of acceptable plastic-made caps is extremely low because of large dimensional errors of the glass-made vials.